The present invention relates to a device for the dynamic stabilization of bones or bone fragments, especially of vertebrae, and comprises at least one longitudinal carrier, which is connected over at least two bone fixation agents attached to vertebral bodies. The bone fixation agents preferably are pedicle screws, which are brought from the rear through the pedicle into the vertebral bodies.
The main indications for a dynamic fixation, especially for one passed through from the rear, are an age-related and/or disease-related degeneration of the integrity of the structure of the spinal column, inflammations, and/or injuries in the region of the intervertebral disk, the ligamentous apparatus, the facet joints, and/or the subchondral bone.
In typical fixation devices, as described in the patents WO 94/00066 (of Schläpfer and Hess), WO 98/25534 (of Schläpfer) and WO 98/52482 (Schläpfer and Hess), the bone fixation agent is connected rigidly with the longitudinal carrier over an interposed connecting element. The connection between the bone fixation agent and the longitudinal carrier is constructed in the form of a ball joint and can be locked in any position. But this means that the fixation device should be fitted anatomically correctly. Moreover, because of this stiffness, these typical fixation devices are used for fusing segments of the vertebrae.
With the stiff connection, the prerequisites are created for a bony fusion of the bridged spinal column segments, but not for a conversion of the movement pattern and stress pattern into one, which reduces the symptoms, promotes the metabolism of the affected structures and is aimed for with the dynamic fixation concept.
A device for the elastically damped connection between the head segments of pedicle screws and a longitudinal carrier is known from the U.S. Pat. No. 5,480,401 of Navas. This known device comprises elastic clamping elements for fixing the spherical head segments of the pedicle screws within the stabilizing device. It is a disadvantage of this known device that the head segment is clamped by friction between the elastic clamping elements, so that the head segment can slip to one side if the torque between the bone fixation agent and the longitudinal carrier is sufficiently high.
The invention is to provide a remedy here.